In wireless communication systems, a mobile station may be comprised of a handset including a microphone and speaker which are used to receive and place calls. Handsets typically require the user to hold the handset close to the user's head so the microphone and speaker are positioned close to the user's mouth and ear, respectively. However, there are times in which the user may desire to use the handset in a handsfree mode, such as when walking or using the handset for an extended period of time. In these circumstances, a headset may be used which connects to the handset and allows the user to operate the handset in a handsfree mode. Additionally, the headset allows the user to operate in a handsfree mode while maintaining privacy between the user and the handset. In addition to a mobile station, other portable devices such as personal digital assistants (PDA), portable music players and similar devices may take advantage of the use of a headset.
Wireless communication systems typically comprise a plurality of base stations and mobile stations that communicate using an over-the-air communication protocol using physical layer technologies such as Code Division Multiple Access (CDMA) technology. As more functionality is added to wireless handsets and other devices, it may be desirable to include a control switch with a headset to allow a user to operate or activate features in the device from the headset. For example, a user could close the control switch to activate a mute function, control playback of an audio file, launch a web browser, or dial a number. Of course, the control switch may activate any number of features, and is not limited to the features listed here.
For the control switch to be functional, a detection circuit may be used. Detection circuits are designed to effectively sense a change in operating current triggered by the opening and closing action of the switch on the headset. Currently detection is done off-chip, requiring extra off-chip components, which increases the cost and complexity of the portable device. Alternatively, a current-to-voltage conversion may be performed and a sample-and-hold circuit may used to store the information. However, this technique performs all functions in the analog domain, and thus requires a high quality operational amplifier, comparator, and low leakage sample-and-hold capacitor. These devices are large and expensive, and thus not desirable. Because the activity time is at least once every 25 ms, it is difficult to design an accurate and power efficient sample-and-hold circuit for the application.
What is needed is a system that detects the open and close action of a mechanical switch and performs the functions in the digital domain. By determining the action of the mechanical switch in the digital domain, a more compact, accurate, and efficient design may be obtained. The system should also be capable of being incorporated on-chip to minimize the complexity and cost of the solution.